Known miniature electric stepping motors comprise a magnetized rotor, a stationary magnetic circuit having spaced polar parts defining an air gap, an electric excitation coil, coupled to the stationary magnetic circuit, and a control device connected to the excitation coil, means for mounting the magnetized rotor for rotation in said air gap so that its poles cooperate with the polar parts of the stationary magnetic circuit, the magnetization of the rotor and the form of the polar parts being such that the rotor has at least one stable, equilibrium position, the control device comprising means for applying to the excitation coil, starting from each stable equilibrium position of the rotor, a control impulse having a first polarity, an amplitude and a width such that the rotor rotates in the said first direction of rotation until it reaches the next stable equilibrium position.
A motor of this kind is capable, by its nature, of operating in opposite directions of rotation depending on the polarity of the impulses applied to the excitation coil. However, owing to production tolerances and the variations of certain parameters, e.g. mechanical load, temperature, supply voltage, one generally renounces to use the possibility of operating the motor in opposite directions of rotation at will and chooses a stable equilibrium position so as to considerably favour one direction of rotation, i.e. so as to increase the work produced by the control impulse in this direction with respect to a position in which the two impulses would involve almost identical energies.